Generally, an electrostatic latent image is formed on a photoreceptor possessing photoconductivity, employing various means, and subsequently, said latent image is developed employing a toner. The resulting toner image is transferred to a transfer material such as a sheet of paper, if desired, and thereafter, copied and printed materials are obtained by fixing the transferred image employing heat, pressure, and the like.
In the above-mentioned process, all of the toner on the photoreceptor is not transferred but about 5 to 20 percent by weight of the toner remain on the photoreceptor. Such residual toner (non-transferred toner) on the photoreceptor has been collected employing a cleaning process, fed to the exterior of the apparatus as toner waste, which has generally not been able to be reused. However, in recent years, the demand for copiers and printers has increased, and further, the demand for high-speed copiers and printers is increasing by leaps and bounds. In such high-speed apparatuses, a large volume of toner waste is generated, which, when disposed of improperly, may pollute the environment. Under such situations, in recent years, investigations on recycling of the above-mentioned toner waste have been widely made, that is, recycling of the toner collected by a cleaning process. If the toner waste can be recycled, the following advantages may be expected; supplied toner can be sufficiently used and the toner can be used effectively. Further, it is possible to eliminate a storage area for storing the toner waste and to reduce the overall dimensions of the apparatus.
However, when conventional toner waste is returned to a development process and is reused as a developer material, adverse effects such as a decrease in reflection image density, an increase in background staining or reversal staining, toner scattering, and the like have resulted.
In response to the demand of such toner recycling, various inventions have been made.
For example, Japanese Patent Publication Open to Public Inspection No. 6-75423 proposes a recycled toner of which properties are improved by broadening the molecular weight distribution of the toner to increase high molecular weight components. Furthermore, Japanese Patent Publication Open to Public Inspection No. 6-75423 proposes a recycled toner of which properties and fixability are improved in such a manner that molecular weight distribution component of toner binders exhibits two peaks and both polypropylene and amide wax are incorporated into the toner.
However, in the above mentioned toners, which are obtained by improving the conventional pulverized toner, undesirable fine toner powder is formed during pulverization, and it is difficult to remove said fine powder employing normal classification means. As a result, fine toner powder remains in the toner. When the toner comprising such a fine toner powder is employed, after development, it is difficult to transfer the fine toner powder on a photoreceptor onto a transfer material due to its strong adhesion to the photoreceptor. When such a toner is fed into a toner recycling system, the fine toner powder is collected by cleaning and returned to the development section. Thus, it is likely to be accumulated in the development section. In the development section, such fine toner powder tends to be fused with the carrier and the like, resulting in a so-called spent phenomenon and further resulting in fusion to the development sleeve and the like. As a result, the charge providing capability of the carrier and the like decreases, resulting in a decrease of the charge amount of toner, and an increase in a charge amount distribution (increase in the amount of weakly chargeable toner, and the like). Finally, background staining tends to occur.
As described above, improvements in the recycled adaptability of the toner prepared by pulverization are limited. At present, toner is not available, which satisfies required needs for such recycled toner, that is, which satisfies needs of developability, fixability at low temperature, lowered offsetting tendency, lowered blocking tendency, and the like, and constantly produces excellent images when toner waste is recycled and reused.
Further, as a means to overcome problems of the above-mentioned fine toner powder, Japanese Patent Publication Open to Public Inspection Nos. 60-31117, 60-107656, and 60-117255 proposes suspension-polymerized toners, which are spherical and have a narrow particle size distribution. However, when these suspension-polymerized toners are recycled, together with external additives such as silica and the like, the external additives are buried into the toner surface due to its spherical shape. As a result, the fluidity of the recycled toner is markedly degraded and the transfer ratio of the toner to a transfer material such as a sheet of paper or the like decreases, and image quality tends to be degraded.
Regarding the shape of toner particles, in order to solve the above-mentioned problems, it is proposed that the toner is deformed so that the toner has an uneven surface rather than a spherically smooth surface. In Japanese Patent Publication Open to Public Inspection No. 7-26207, a method to solve these problems is proposed, in which the degree of shape deformation of toner is defined employing a shape coefficient.
In said patent, methods are disclosed in which modification is carried out by fine resin particles adhere onto the surface of suspension-polymerized toner, or deformation is carried by allowing suspension-polymerized toner to swell while immersed in a solvent, followed by drying under reduced pressure.
However, when the deformation is carried out by fine resin particles adhere onto the surface of said suspension-polymerized toner, fine resin particles adhered onto the toner surface are released from the surface during the agitation of the developer material in the development unit, and charges concentrate onto the fine resin particles on the surface, which broadens the charge amount distribution. As a result, toner scattering on finished images is increased to deteriorate the definition of text images. In addition, the properties of the surface-deformed toner, prepared by immersing a suspension-polymerized toner into a solvent, tend to be unstable due to differences in production lots, and problems related to unstable image quality occur.
Furthermore, the surface of a photoreceptor is coated with a resin. Therefore, specifically, the performance of a resin is critical and resins having excellent durability have been desired. Recently, employed as resins to improve these characteristics have generally been polycarbonate resins (hereinafter referred to as bisphenol Z polycarbonate) in which bisphenol Z (polycarbonate in which the central carbon atom of bisphenol A is modified with a cyclohexyl ring) is used as the main skeleton, which are used as a binder in the surface layer. As a result, the surface abrasion of a photoreceptor is minimized during the development process as well as the cleaning process, and it becomes difficult to remove the toner adhered onto the photoreceptor surface.
Namely, when such a photoreceptor is employed in an image forming apparatus using a recycling system, it is impossible to remove fine toner particles adhered onto the photoreceptor surface. Further, due to causes that fine toner particles adhered on the photoreceptor may not be removed and a portion of these fine toner particles adhere and stain the charging member and the like, in the finished images, a phenomenon tends to occur in which image defects consisting of black streaks or many white spots are formed over the entire image.
On the other hand, electrophotography is employed not only in monochromatic copiers, but also in the field of computer output terminal printers, color copiers, color printers, and the like. As electrophotography is increasingly employed, demand for image quality has been raised.
In order to improve overall image quality, various proposals have been made in which image quality is improved by decreasing the size of toner particles, and no effort will be made to enumerate them. As a technique corresponding to the decrease in the size of toner particles, so-called polymerization methods for toners are known. One of them is a production method of a polymerized toner, comprised of a fusion of resin particles with colorant particles, described in Japanese Patent Publication Open to Public Inspection No. 63-186253, and the like, which discloses a technique capable of making particles of undefined shape. However, when only this technique is employed, it is possible to make particles of undefined shape but is not capable of making shape distribution stable. As a result, since the shape distribution is broad, a chargeability distribution also broadened, resulting in unstable development. Further, during transfer, problems with a decrease in transfer efficiency occur due to the effect of the chargeability distribution.
Furthermore, as the particle diameter decreases in the particle diameter distribution, the adhesion power of the particle itself to a carrier becomes stronger under the same charge amount due to the decrease in the weight of the particle itself. Owing to that, in a toner having the distribution of chargeability, a difference in detaching from a charge providing member such as a carrier tends to occur. As a result, the developability is not stabilized, and further, during transfer, a problem with uneven transfer tends to occur.
Further, in conventional diameter-decreased toner, many toner particles having a high van der Waals force exist. Thus charge providing capability decreases, and weakly chargeable toner as well as excessively charged toner are generated.
As a result, when employed over a long period of time, a background staining results on printed images. Accordingly, problems occur in which a development unit or carrier in two-component development is stained, and subsequently its durability decreases.
A diameter decreased toner results in a charge rising problem. In order to solve this problem, as proposed in Japanese Patent Publication Open to Public Inspection No. 9-96919, investigations have been carried out in which the specific surface area of toner particles is increased to improve the charging rise. When this method is employed, the charging rise is fairly improved. However, even in this case, the uniformity of shape is not sufficient in conventional toner, which results in problems with development stability, transfer stability, and the like. As a result, variation in its performance is large, and specifically, in development in which high resolution is required, the resulting performance is not sufficient.